Polymers made from a Diels-Alder reaction are briefly described in the art. U.S. Pat. No. 3,334,071 teaches the formation of polyimides from dimaleimides and bis(fulvenes). An aliphatic or aromatic compound is end-capped with a maleimide radical which reacts with a fulvene end-capped compound to produce an alicyclic endomethylene linkage in the polymer backbone chain.
U.S. Pat. No. 2,971,944 teaches the preparation of maleimide polymers by the Diels-Alder reaction of a N,N'-bis(maleimide) with a thiophene dioxide to produce a monomeric adduct which can then be homopolymerized. During the Diels-Alder reaction of the thiophene dioxide with the bis(maleimide), sulfur dioxide is evolved prior to the polymerization reaction.
U.S. Pat. No. 3,074,915 teaches a similar polymeric reaction, however, in place of the thiophene dioxide, a substituted alpha-pyrone is used. Upon reaction of the substituted alpha-pyrone with the bis(maleimide), to produce the monomeric Diels-Alder adduct, carbon dioxide is given off.
U.S. Pat. No. 2,890,206 teaches a maleimide polymer produced by the polymerization of a Diels-Alder adduct which is produced by the reaction of an N,N'-bis(maleimide) with a cyclopentadieneone. The Diels-Alder adduct contains an endocarbonyl bridge which is destroyed by heating above about 150.degree.C. The resulting adduct is then polymerized.